User: a level of production in which the marginal production decreases with new inverstment

Weegy: Fixed cost is the amount of money a store must pay regardless of demand. [ In the case of your choices, the fixed cost would be the rent because the store must pay for the rent regardless of the number of customers that come to the store.
Short-term employees can vary
Advertising can vary
Inventory can vary
all three are variable costs.
BOL ] Expert answered|sportyduke|Points 0|